Background: Ultrasound (US)-guided central venous catheterization has become widely used due to the availability of small high-resolution US devices. Since US-guided central venous (CV) catheterization can be performed while confirming the location of the puncture needle and the structure around the vein, there have been many reports on the high level of safety, but complications have been happened by overconfidence of US images. US devices are also used for evaluation of lung diseases. We report a case of pneumothorax caused by CV port placement that was detected quickly by US.
Case report: A 60-year-old woman was scheduled diagnostic laparoscopy and CV port placement under general anesthesia. For CV port placement, the assistant obtained a short axis view of the right subclavian vein with US, and the operator performed puncture using the out-of-plane method. The needle was inserted up to its base without confirmation of the tip. Although the needle tip was also not visualized on the second puncture, an image showing compression of the subclavian vein by the needle was obtained and the guidewire was placed by the penetration method. Then the CV port was implanted by the usual process, and there was no change in ventilation and oxygenation. We performed lung ultrasonography because pneumothorax was suspected due to the puncture procedure. The US image showed a lack of lung sliding and a barcode sign at the right anterior thoracic region, therefore we diagnosed as a pneumothorax. Then we tried to find out a lung point to estimate the severity of the pneumothorax, but no lung point was found in the lateral thoracic region. This US scan indicated a severe pneumothorax, therefore a chest tube was quickly placed. 
Discussion: When performing US-guided CV catheterization, serious complications can occur without US images of the puncture needle tip. Safe puncture is not possible without a good understanding of the characteristics of US-guided puncture. To visualize the target vein and puncture needle on the US image is important. This can be achieved by correct handling of US probe and puncture needle. It is risky to just focus on the US images. 
Learning points: Attention must be given to possible complications such as pneumothorax that can occur if US-guided CV puncture is performed improperly. Pneumothorax is easily diagnosed by lung ultrasound, thus US should be used to check for pneumothorax after performing CV catheterization.

Ultrasound detection of pneumothorax caused by improper ultrasound-guided central vein puncture